<template>
  <div class="pagination">
    <button @click="changePageNo(pageNo-1)" :disabled="pageNo === 1">上一页</button>
    <button @click="changePageNo(1)" v-show="startEnd.start !== 1">1</button>
    <span v-show="startEnd.start > 2">···</span>

    <!-- 连续分页 -->
    <button @click="changePageNo(index + startEnd.start)" :class="{active:pageNo === index + startEnd.start}" v-for="(n,index) in (startEnd.end - startEnd.start + 1)" :key="index">
        {{ index + startEnd.start }} 
    </button>

    <span v-show="startEnd.end < totalPage -1">···</span>
    <button @click="changePageNo(totalPage)" v-show="startEnd.end !== totalPage">{{totalPage}}</button>
    <button @click="changePageNo(pageNo+1)" :disabled="pageNo === totalPage">下一页</button>

    <span>共 {{total}} 条</span> 
  </div>
</template>

<script>
//1. 计算 正常情况 连续分页： pageNo - （continues-1）/2
//2. 计算 不正常情况 连续分页：  当 传入的 continues >  totalPage ,start = 1  end = pageTotal
//3. 计算 不正常情况 连续分页: 当 start  < 1 ;start = 1;  end = continues
//4. 计算 不正常情况 连续分页: 当 end  > totalPage ;start = totalPage - continues +1;  end = totalPage

export default {
  name: "Pagination",
  props:{
    total:{  //总数
        required:true,
    },
    pageSize:{  //每页展示数量
        type:Number,
        required:true,
    },
    pageNo:{ //当前页码
        type:Number,
        required:true,
    },
    continues:{  //连续页数
        type:Number,
        default:5,
    },
    changePageNo:{
      type:Function,
      required:true
    }
  },
  computed:{
    //计算总页码
    totalPage(){
        return Math.ceil(this.total/this.pageSize);
    },
    //计算连续分页初始值和结束值
    startEnd(){

        let {pageNo,pageSize,continues,totalPage} = this;
        // 初识值
        let start = 0;
        //结束值
        let end = 0;
        //连续页码 > 计算出的总页码
        if(continues > totalPage){
            start = 1;
            end = totalPage;
        }else{
             //计算
            start = pageNo - (continues-1)/2;
            end = pageNo + (continues-1)/2;
            //计算 不正常情况 连续分页: 当 start  < 1 ;start = 1;  end = continues
            if(start < 1){
                start = 1;
                end = continues;
            }
            // 计算 不正常情况 连续分页: 当 end  > totalPage ;start = totalPage - continues +1;  end = totalPage
            if(end > totalPage){
                start = totalPage - continues + 1;
                end = totalPage;
            }


        }
       
        return {
            start,
            end
        }
    }
  }
};
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;

  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: gray;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #c81623;
      color: #fff;
    }
  }

  span {
    display: inline-block;
    line-height: 28px;
    font-size: 14px;
    color: gray;
    vertical-align: middle;
  }
}
</style>